1. Technical Problem
The invention relates to novel compounds from the class of the macrolide antibiotic oleandomycin, tointermediates for the preparation thereof, to a process for preparing them as well as to pharmaceutically acceptable addition salts thereof with inorganic or organic acids.
2. Prior Art
Oleandomycin is a macrolide antibiotic (U.S. Pat. No. 2,757,123) having an activity spectrum similar to that of erythromycin A. The oleandomycin structure is characterized by a 14-member lactone ring with a keto group in C-9 position, by the sugar desosamin in C-5 position and by the sugar oleandrose in C-3 position as well as by three OH groups. It differs from other polyoxo macrolides by an exocyclic epoxide ring on C-8 atom. Earlier investigations (JACS 82, 3225-3227, 1960; JOC 51, 5397-5400, 1986) showed its exceptional sensitivity both in acidic and basic conditions. In an acidic medium C-8 epoxide is opened, oleandrose is cleaved and a contraction of the aglycone ring takes place. The action of a base causes a dehydratation of H-10 and OH-11 under the generation of C-10/C-11 double bond to give anhydrooleandomycin. All these transformations cause a loss of the antibiotic action.
It is known that similar transformations at erymromycin A with OH groups participating are successfully inhibited by O-methylation thereof (Watanabe Y. and al, U.S. Pat. No. 4,331,803, 5/1982). By the reaction of erymromycin A with benzyloxycarbonyl chloride and then by methylation of the obtained 2xe2x80x2-O,3xe2x80x2-N-bis(benzyloxycarbonyl)-derivatives, after elimination of protecting groups and N-methylation, there are obtained, in addition to 6-O-methyl erythromycin (CLARITHROMYCIN), significant amounts of 11-O-methyl erythromycin and polysubstituted analogues (Morimo S. et al, J. Antibiotics 1984, 37, 187). Clarithromycin is significantly more stable in an acidic medium than erythromycin A and shows enhanced in vitro activity against Gram positive bacterial strains (Kirst H. A. et al. Antimicrobial Agents and Chemother., 1989, 1419). Similarly, also a series of O-methyl derivatives of azythromycin was synthesised (Kobrehel G. et al, U.S. Pat. No. 5,250,518, 5/1993).
Our efforts to inhibit the formation of an inactive anhydrooleandomycin by O-methylation of C-11 hydroxyl group, retroaldol fragmentation, dehydratation and isomerisation took place and led to a series of linear and cyclic derivatives of oleandomycin, not yet disclosed so far, which may serve as intermediates for chimeric oleandomycins with potential biological action.
The synthesis of these derivatives involves a reaction of oleandomycin with benzyloxycarbonyl chloride to obtain 2xe2x80x2-O,3xe2x80x2-N-bis(benzyloxycarbonyl)-3xe2x80x2-N-demethyl oleandomycin, a reaction with methyl iodide in the presence of sodium hydride, an elimination of protecting groups on 2xe2x80x2 and 3xe2x80x2 positions and reductive 3xe2x80x2-N-methylation.
Oleandomycin derivatives according to the present invention and their pharmaceutically acceptable addition salts with inorganic or organic acids, methods and intermediates for the preparation thereof have not been disclosed in Prior Art.
Novel derivatives of oleandomycin of the general formula (I) 
wherein
R1 has the individual meaning of xe2x80x94CH2CH3 group, of a fragment of the formula (II), together with R2 has the meaning of a fragment of the formula (III) or together with R4 has the meaning of a fragment of the formula (IV) or a fragment of the formula (V) 
R2 together with R3 has the meaning of a ketone or together with R1 has the meaning of a fragment of the formula (III),
R3 has the individual meaning of OH group or together with R2 has the meaning of a ketone,
R4 has the individual meaning of a methyl group, or together with R1 has the meaning of a fragment of the formula (IV) or of a fragment of the formula (V),
R5 has the individual meaning of hydrogen or a benzyloxycarbonyl group,
R6 has the individual meaning of hydrogen, a methyl group or a benzyloxycarbonyl group,
and their pharmaceutically acceptable addition salts with inorganic or organic acids, are obtained as follows.
Fragment IV is one of one of sixteen diasteroisomers of fragment V. As is known to persons of skill in the chemical arts, a wedge-shaped bond represents bonding to a group projecting above the plane of the paper. As is known to persons of skill in the chemical arts, a stippled bond represents bonding to a group projecting below the plane of the paper. For purposes of lexicography, we individually name the sixteen diastereoisomers of Fragment V with respect to the projection of the various bonds starting with the bond closest to the top of the page, With reference to fragment IV, the bond to methyl nearest the top of the page, projects up (U), the bond to hydroxyl projects up (U), continuing down the page, the bond to methyl projects down (D), and the bond to methyl towards the bottom of the page projects down (D). Thus we name Fragment IV, the UUDD diastereoisomer of Fragment V, Fragment V1. Retaining the same naming convention, there are four UU diastereoisomers (UUDD, V1; UUUD, V2; UUDU, V3; UUUU, V4). There are four DD diastereoisomers (DDDD, V5; DDUD, V6; DDDU, V7; DDUU, V8). There are four DU diastereoisomers (DUDD, V9; DUUD, V10; DUDU, V11; DUUU, V12). There are four UD diastereoisomers (UDDD, V13; UDUD, V14; UDDU, V15; UDUU, V16) 
By subjecting oleandomycin of the formula (VI) to a reaction with benzyloxycarbonyl chloride in the presence of bases, preferably sodium hydrogen carbonate, in a solvent inert in the reaction, preferably benzene or toluene, there is obtained 2xe2x80x2-O,3xe2x80x2-N-bis(benzyloxycarbonyl)-3xe2x80x2-N-demethyl-oleandomycin of the general formula (I), wherein R1 together with R4 has the meaning of a fragment of the formula (IV), R2 together with R3 has the meaning of a ketone and R5 and R6 are the same and have the meaning of a benzyloxycarbonyl group.
Step 2:
By a reaction of 2xe2x80x2-O,3xe2x80x2-N-bis(benzyloxycarbonyl)-3xe2x80x2-N-demethyl-oleandomycin from Step 1 with 1.3-3.25 equivalents of the corresponding methylation agent, preferably methyl iodide, and 1.1-3.75 equivalents of the corresponding base, preferably sodium hydride, at a temperature from xe2x88x9215xc2x0 C. to room temperature, preferably at 0-5xc2x0 C., in an appropriate aprotic solvent or solvent mixture, preferably DMSO-THF=1:1, and by separation on a silica gel column in the system toluene-ethyl acetate=1:1 there is obtained
a compound 2A of the general formula (I), wherein R1 has the individual meaning of xe2x80x94CH2CH3 group, R2 together with R3 has the meaning of a ketone, R4 is a methyl group and R5 and R6 are the same and have the meaning of a benzyloxycarbonyl group,
a compound 2B of the general formula (I), wherein R1 together with R4 has the meaning of a fragment of the formula (V), R2 together with R3 has the meaning of a ketone and R5 and R6 are the same and have the meaning of a benzyloxycarbonyl group, and
a compound 2C of the general formula (I), wherein R1 has the individual meaning of a fragment of the formula (II), R2 together with R3 has the meaning of a ketone, R4 is a methyl group and R5 and R6 are the same and have the meaning of a benzyloxycarbonyl group.
The relative ratio of chromatographically homogenous products depends upon the equimolar ratio of reactants.
Step 3:
Each of the oleandomycin derivatives from Step 2 is separately subjected to a hydrogenolysis reaction in order to eliminate protecting benzyloxycarbonyl groups in 2xe2x80x2 and 3xe2x80x2 positions according to the method by E. H. Flynn et al (Journal of American Chemical Society, 77, 3104, 1950). Hydrogenolysis is carried out in a lower alcohol solution, preferably in ethanol, in the presence of NaOAc/HOAc buffer (pH 5), with a catalyst such as palladium black or palladium on carbon, under hydrogen pressure of 105 Pa at room temperature to obtain, respectively,
in case of 2A, a compound 3A of the general formula (I), wherein R1-R4 have the meanings as given for the compound 2A and R5 and R6 are the same and have the meaning of hydrogen, and
in case of 2B, a compound 3B of the general formula (I), wherein R1-R4 have the meanings as given for the compound 2B and R5 and R6 are the same and have the meaning of hydrogen, and
in case of 2C, a compound 3C of the general formula (I), wherein R1 together with R2 has the meaning of a fragment of the formula (III), R3 is an OH group, R4 is a methyl group and R5 and R6 are the same and have the meaning of hydrogen.
Step 4:
Each of the 3xe2x80x2-N-demethyl derivatives of oleandomycin from Step 3 is subjected to reductive N-methylation in 3xe2x80x2 position with 1-6.2 equivalents of formaldehyde (36%) in the presence of 1-4.2 equivalents of formic acid (98-100%) or some other hydrogen source, in a solvent inert in the reaction such as halogenated hydrocarbons, lower alcohols or lower ketones, preferably chloroform, at the reflux temperature of the reaction mixture, to obtain, respectively,
in case of 3A, a compound 4A of the general formula (I), wherein R1-R4 have the meanings as given for the compound 2A, R5 is hydrogen and R6 is a methyl group, and
in case of 3B, a compound 4B of the general formula (I), wherein R1-R4 have the meanings as given for the compound 2B, R5is hydrogen and R6 is a methyl group, and
in case of 3C, a compound 4C of the general formula (I), wherein R1-R4 have the meanings as given for the compound 3C, R5 is hydrogen and R6 is a methyl group.
Fragments of the formulas (II), (III) and (V) are shown without space orientation of the bonds and define all combinations of orientation of bonds in order to comprise all possible stereoconfigurations, i.e. epimers.
Pharmaceutically acceptable addition salts which are also an object of the present invention, are obtained by reacting novel oleandomycin derivatives of the general formula (I) with an at least equimolar amount of a corresponding inorganic or organic acid such as hydrochloric, hydroiodic, sulfuric, phosphoric, acetic, propionic, trifluoroacetic, maleic, citric, stearic, succinic, ethylsuccinic, methanesulfonic, benzenesulfonic, p-toluenesulfonic, laurylsulfonic acids etc., in a solvent inert in the reaction. Addition salts are isolated by filtration if insoluble in the solvent inert in the reaction, by precipitation by means of non-solvents or evaporation of solvents, most often by a lyophilization process.